The present invention relates generally to data compression techniques, and more particularly to a method and system for decoding a digital signal sampled at intervals variable inversely as a function of the instantaneous frequency of the analog signal.
Many attempts have hitherto been made to reduce the amount of information to be stored in a recording medium or transmitted over telephone lines to a distant end. A known data compression technique includes a method whereby the amplitude of analog signals is logarithmically compressed, and a method known as delta modulation in which the differential component of the analog signal is detected for transmission and the signal is integrated for recovery at the receiving end. In either of these known methods, the analog signal is sampled at a constant frequency which is at least twice the highest frequency of the analog signal to prevent foldover distortion. However, due to the constant sampling frequency quantum noise occurs in the known data compression system over the the bandwidth of the recovered signal.
According to a data compression system, as shown and described in Japanese Patent Publication (Tokkaisho) No. 56-155998, the sampling interval is determined by the amount of deviation of the original signal from the previously sampled analog value so that the deviation is smaller than a predetermined value of the ratio of the original to the sampled value. While this data compression system is satisfactory under certain circumstances, a disadvantage is that details of the original waveform are not satisfactorily recovered.